Magnesium chloride (MgCl.sub.2) powder covered with titanium chloride (TiCl.sub.3, TiCl.sub.4) is an original material well-known as Ziegler-Natta type catalysts. The yield of these catalysts depends among other things on the particle size of the original material; the finer the particles are, the higher the yield is. There is thus a need for an improved process for the production of catalyst powders, more particularly of MgCl.sub.2 powder covered with titanium chloride that allows to obtain a very fine granulometry. In fact, it is particularly difficult to obtain a very fine granulometry powder by pulverizing MgCl.sub.2 under anhydrous conditions, although this fineness is desired when MgCl.sub.2 is used in the catalysts preparation.
The morphology of polymer grains--and consequently, the polymer apparent density--is among other things determined by the catalyst morphology. It is then very desirable to be able to control the morphology of the catalyst powder that is ideally spherical.
Patent GB-1279208-A (Standard Telephones; equivalent to DE-22 17951-A, Deutsche ITT ) discloses a process of powder production consisting in vaporizing the material or its components in an inductive coupling plasma (ICP) then in condensing the vapor.
U.S. Pat. No. 4650778-A (Klabunde et al.) shows a process for the preparation of halogen metal particles consisting in vaporizing them by heating, then in condensing the vapor in the presence of a reactive diluent. The obtained solid must be activated by metal alkyls to be used as catalysts of olefin polymerizations.
Belgian Patent BE-1005737-A (filed on Aug. 5, 1992 and published on Nov. 1, 1994) claims a process for the production of magnesium powder, characterized in that it consists essentially in introducing rough powder of magnesium chloride, with or without titanium chloride in a plasma torch and cooling the vapor in order to collect a very fine granulometry powder, eventually by covering this powder with an electron donor during the cooling.
An object of the present invention is to provide an improved process for the production of powder Catalysts comprising MgCl.sub.2 and titanium chloride and having a very fine granulometry.
Another object of the invention is to provide an improved process for the production of powder catalysts comprising MgCl.sub.2 and titanium chloride and having a controlled morphology.
Another object of the invention is to supply a powder catalyst comprising MgCl.sub.2 and titanium chloride, having a very fine granulometry and having a controlled morphology.
Another object of the present invention is to provide an improved olefins polymerization process that uses as a catalyst a MgCl.sub.2 titanium chloride based powder obtained according to the invention.